Litz wire size for coils

[Darin]

I have been looking for some info I think I read it on here a while back but have not been able to fine it again. I have used the search, read multiple post, etc.
It was a list of litz wire size and what worked best for different coils
Can anyone tell what size litz wire I should use to make a basket coil for my MPP to search for gold nuggets.

[baum7154]

I don't know about the litz wire specs but the best monocoils I know of and have built several of I have detailed in the Chance PI Coil thread of this same forum. Technically these coils are called 3DSS coils and this designation refers to the 3 Dimensional winding pattern with the benefit of Self Shielding. The latest coil detailed in that thread the Racetrack 3:1 coil operates below 7us with proper damping and is specifically designed for small gold detection.

Good luck,

Dan

[Beav]

Do you mean this link, Darin? : http://www.newenglandwire.com/produc...es/theory.aspx
I found it on the following thread here: http://www.geotech1.com/forums/showt...r-Pi-Detectors
Post #16

Beav

[Darin]

What I remember reading was a list someone had typed out with the wire size and which size worked best for coils use.
Something like this but this info may not be correct it is just an example off the top of my head.

wire size / coil speed / coil use

175/46 / medium / good for coins

330/30 / fast coil / makes good coil for hunting gold nuggets

660/46 / really fast coil / makes good coil for hunting gold nuggets

[Darin]

What I am trying to do is find out what wire I should use to make coils for my MPP to search for small and large gold nuggets and get the most depth.

I am thinking maybe a round 4" , 7" 0r 8" , 12" and maybe a 16", 18" or 20".
would a round bunch type or the 3DSS like in the chance pi coil thread work better?
I know the 3DSS are self shielding but just looking for info and advise from those with more experience.

Thanks

[6666]

What I remember reading was a list someone had typed out with the wire size and which size worked best for coils use.
Something like this but this info may not be correct it is just an example off the top of my head.

wire size / coil speed / coil use

175/46 / medium / good for coins

330/30 / fast coil / makes good coil for hunting gold nuggets

660/46 / really fast coil / makes good coil for hunting gold nuggets

That would be super handy if it can be found.

[baum7154]

What I am trying to do is find out what wire I should use to make coils for my MPP to search for small and large gold nuggets and get the most depth.

I am thinking maybe a round 4" , 7" 0r 8" , 12" and maybe a 16", 18" or 20".
would a round bunch type or the 3DSS like in the chance pi coil thread work better?
I know the 3DSS are self shielding but just looking for info and advise from those with more experience.

Thanks

------------------------
I think it would be helpful to determine what size of small gold nuggets you will be trying to detect. For example nuggets in the range of 10 grains would need a fast coil of about 8" in order to see them at about 4" of depth. A 12" or larger coil might very well miss it. A 5 grain nugget would likely need a 6" coil or even smaller depending on the detector. Large nuggets of a gram (15 grains)or more are not difficult for an 8" round coil to see. There are trade offs when determining what size of coil to use, larger ones cover ground more quickly and can see large targets at greater depth, but have difficulty on small targets. Typically optimum detection depth is about the same as the coil RADIUS.

Regarding a bunch wound coil vs a 3DSS coil for the specific purpose of small gold (5 to 10 grains)detection, I believe a properly constructed 3DSS is faster and more sensitive compared to a properly shielded bunch wound coil of identical diameter and inductance.

I hope this helps a little.

Dan

[Darin]

That would be super handy if it can be found.

I thought I saw it on this form, but I have not found it yet. I will keep looking. If I can find it again where ever it was that I came across it I will copy it and post it on this form.

[Darin]

------------------------
I think it would be helpful to determine what size of small gold nuggets you will be trying to detect. For example nuggets in the range of 10 grains would need a fast coil of about 8" in order to see them at about 4" of depth. A 12" or larger coil might very well miss it. A 5 grain nugget would likely need a 6" coil or even smaller depending on the detector. Large nuggets of a gram (15 grains)or more are not difficult for an 8" round coil to see. There are trade offs when determining what size of coil to use, larger ones cover ground more quickly and can see large targets at greater depth, but have difficulty on small targets. Typically optimum detection depth is about the same as the coil RADIUS.

Regarding a bunch wound coil vs a 3DSS coil for the specific purpose of small gold (5 to 10 grains)detection, I believe a properly constructed 3DSS is faster and more sensitive compared to a properly shielded bunch wound coil of identical diameter and inductance.

I hope this helps a little.

Dan

Thanks Dan this does help. Seems I'm looking the right direction.
I have two friends with gold claims they detect on using GPX 5000's and ATX with mono coils that range in size from 8" to 20". They find gold from 3 - 4 grains to a little larger than a oz. that I have seen.
I was thinking make 3DSS round coils ranging in size a 4" , 8" , 12" , as round coils seem to get a little better depth if I am correct and that should give me good range in coil size for say 3-5 grain gold and larger. I am thinking a larger coil maybe a 20" as they do find gold with theirs but seems to me you would pass over small grain gold and need to go back over the area with smaller coils but I guess that would be the thing to do anyway.

Now just to find the right wire and size for each coil or can I use the same size for all the coils?
And how difficult is litz wire to work with soldering?
Any thoughts on Teflon vs litz wire for 3DSS coils?

Thanks

Darin

[chemelec]

Litz Wire is Fairly easy to Solder, Especially if you have a Solder Pot to Tin It.
Most Litz wire is just wrapped a bit with a nylon thread to hold it together.

The individual wires in the Litz wire, can have various Coatings, including a Teflon Coating, which is probably the best coating.

[baum7154]

[QUOTE=Darin;212061]Thanks Dan this does help. Seems I'm looking the right direction.
I have two friends with gold claims they detect on using GPX 5000's and ATX with mono coils that range in size from 8" to 20". They find gold from 3 - 4 grains to a little larger than a oz. that I have seen.
I was thinking make 3DSS round coils ranging in size a 4" , 8" , 12" , as round coils seem to get a little better depth if I am correct and that should give me good range in coil size for say 3-5 grain gold and larger. I am thinking a larger coil maybe a 20" as they do find gold with theirs but seems to me you would pass over small grain gold and need to go back over the area with smaller coils but I guess that would be the thing to do anyway.

Now just to find the right wire and size for each coil or can I use the same size for all the coils?
And how difficult is litz wire to work with soldering?
Any thoughts on Teflon vs litz wire for 3DSS coils?
------------------------------------------------------------
You are correct that round mono coils do get better depth than other shapes of mono coils I have tried. I'd guess that your friends 20" coils can look deeper for big nuggets but not for the tiny nuggets.

Regarding the wire type and size, for 3DSS coils I only use PTFE or TEFLON 600V insulated in either 24awg or 26awg. The Teflon wire I use is always stranded and silver plated, not silver clad. Silver cladding bonds the strands together and is too much silver causing excessive eddy currents to form. The 3:1 3DSS Racetrack 328uh coil recently posted in the Chance PI Coil thread does operate at 7us of sample delay and uses 24awg stranded silver plated wire. I have not tried to build a 3DSS coil with Litz wire, might be worth a try.

Regards,
Dan

[Darin]

I don't really know what size gold they find with the 20" coils, I just know they have them for both the GPX 5000 and the ATX. Just seems to me that it would be hard for a 20" coil to detect a piece of gold in the 3 - 5 grain size range but I have never done it so I cant say. Hopefully I will have my detector going and be able to go with them this year and find out.
Thanks for the info on the silver plated and the silver clad. That's one reason I was looking at litz wire because I read silver caused excessive eddy currents and didn't see any tinned Teflon wire. I have some 330/46 litz coming, thought I would give it a try. Now I know I can use silver plated I'll look for that too later may try it and compare it to the litz and see if one is better than the other.

Thanks again

Darin

[FatBob]

I found some info a few years back on Litz for MD's. See below;

Litz wire for a metal detector fast coil should be made up of many individual small (44-48 AWG) Polyurethane-Nylon coated wires. Served means that the entire Litz bundle of small wires is wrapped with a nylon textile or yarn for added strength and protection.




Litz wire is designed to minimize the power losses exhibited in solid conductors due to "skin effect". Skin Effect is the tendency of radio frequency current to be concentrated at the surface of the conductor. Litz wire reduces this effect by increasing the amount of surface area without significantly increasing the size of the conductor.




Litz wire composed of many strands of finer wires is best for fast coils. Polyurethane-Nylon coating is the best for soldering because doesn’t require pre-stripping before soldering. It’s hard to strip enamel coating off of 330 individual 44-48 AWG wires for soldering.




Frequency use vs. AWG size of the individual wire strands used within the Litz bundle.
All Values in KHz; a fast coil should be in the 800-3200 kHz range.
1 To 10.0 - 30 AWG
10 To 50.0 - 33 AWG
50 To 100.0 - 36 AWG
100 To 200.0 - 38 AWG
200 To 400.0 - 40 AWG
400 To 800.0 - 42 AWG
800 To 1600 - 44 AWG ------ Fast coil
1600 To 3200 - 46 AWG ----- Fast coil
3200 To 5000 - 48 AWG ----- Hard to find




There are several listings on eBay for Litz wire. The larger (mm) diameter listed in advertisements is normally the overall wire plus serving/insulation measurement. Litz wire made up of 330 strands of #46 AWG (330/46) or (250/46) would be approximately equivalent to an overall 22 AWG solid wire size. Litz 175/46 is approximately equivalent to 24 AWG. These sizes would be good for a fast coil.


Smaller wire will reduce coil capacitance a small amount and be a little faster. I haven't seen any literature on comparisons of coils wound with different size Litz wire. With this modified basket weave there probably is not much difference since there is no parallel wires as wound in commercially built Litz metal detector coils.


Smaller overall wire size will increase the resistance of the coil which results in increasing the time constant of the coil (current charge time) for each transmit pulse. This in turn will limit the pulse repetition frequency (transmit pulses per second). There is a lot of leeway and trade-offs but its good to build in some margins for experimenting with different charge currents, pulsewidths and pulses per second rates.

[6666]

Here is some info on litz wire, PDF table gives nearest equivalent AWG size.,
and a bunch of formula's
http://www.litz-wire.com/technical.php

[godigit1]

Hi
I was looking a a Skin effect calculator and its interesting that at 1000 Hz the Skin effect is 2.4 mm.
When jumping to 2000 Hz the effect is cut in half to 1.70 mm, then as you increase all the way to 5000 Hz =1.07 mm .
Not much gain after 2000 Hz .63 mm in 3000 Hz ?
When I finally get to increasing the pps on my MPP, I'm going to step it at 2000 and see what benefit I get there versus taking it all the way to 5000 pps.
There are some nice frequency to litz wire size recommendations at the site "The litz people" as well as some calculators. (Hope thats Ok to post).

Good Luck